WATCH: The U.S. ambassador to Moscow says next week's NATO Summit in Warsaw will bolster the Western alliance's defensive response to counter Russia's aggression in Ukraine. In an interview with RFE/RL in the Russian capital on June 27, Ambassador John Tefft said that NATO remains the "most effective alliance man has ever put together." (RFE/RL's Russian Service)

The U.S. ambassador to Russia has tried to allay Moscow's concerns about NATO's intentions ahead of a crucial summit next week while offering an impassioned defense of the alliance, which he says has been forced to respond to Kremlin aggression in Ukraine.

In a June 27 interview with the Russian-language services of RFE/RL and VOA, John Tefft also repeated U.S. warnings about recent Russian overflights of U.S. Navy ships and Air Force jets, saying the maneuvers were needlessly provocative.

His comments come ahead of the July 8-9 summit in Warsaw, where NATO leaders are expected to endorse a substantial increase in forces in Poland and the Baltic states, members on the alliance's eastern flank that were under Moscow's domain during Soviet times.

The deployments are aimed at reassuring NATO allies who are increasingly anxious about Russia's intentions in Eastern Europe following its annexation of Ukraine's Crimean Peninsula in 2014 and the ensuing war between Kyiv's forces and Russia-backed separatists in eastern Ukraine.

The Kremlin has complained for years that NATO leaders broke a promise not to expand eastward into former Soviet bloc countries in the 1990s, accusations that the alliance calls baseless.

Tefft repeated Western assurances that Moscow should not view NATO expansion as an act of aggression but said the increase in forces in Eastern Europe was a response to Russia's actions in Ukraine.

"NATO is a defensive alliance, and I say that everywhere I can here in Russia. It's not an offensive organization," he said.

"The response that NATO has prepared for the summit...is a direct response to what had happened here, what had happened in Crimea and east Ukraine in 2014," Tefft added.

Tefft insisted the system was not designed to attack Russia, though Moscow has rebuffed U.S. and Western assurances and threatened unspecified countermeasures.

"We have talked to the Russian side; they have walked out of talks. We have offered to set up NATO-Russia facilities to show how these things would work to be. It would be, in effect, a confidence-building measure," he said. "Russia has not accepted any of those [offers]."

He said NATO remained an important force for stability in Europe and elsewhere. Asked about the criticism of presumptive Republican presidential candidate Donald Trump, who called NATO "obsolete," Tefft defended the alliance while stressing that he was not offering support for any single candidate in the election.

"You shouldn't give up on a strategic system, an organization -- in this case, I think the most effective defensive alliance man has ever put together. You don't give up on those kinds of things," he said.

Since the Crimean annexation and the outbreak of violence in eastern Ukraine, U.S. and Western allies have stepped up patrols and reconnaissance missions along Russia's borders. Moscow has responded by sending jets to buzz the ships or shadow them with naval vessels.

Tefft said the high-speed maneuvers Russian pilots had used increase the potential for mishap or misunderstanding.

"No matter how good the pilots are, we try to say, 'Let's stay away from doing these really provocative actions.' It may be legal, but if it is provocative or trying to buzz a ship -- as they were doing up in the Baltic Sea -- that is just dangerous and, really, there is no place for that, I think, in the modern world," he said.

Increasing Isolation

Tefft also lamented Russia's refusal to resume student exchanges with the United States under the Future Leaders Exchange (FLEX) program that Russia ended its participation in two years ago.

Among the reasons cited by Russian officials for shuttering the program was a same-sex American couple that established guardianship over a Russian high school student who was in the United States on the program.

The move was "cutting young people and others off from access to the rest of the world," Tefft said.

He repeated past criticism of Russian laws that have squeezed nongovernmental organizations, saying that even groups that are pointedly nonpolitical have had their activities curtailed, such as those advocating for HIV or AIDS victims in Russia.

"We think civil society is a fundamental component of democratic government. People ought to -- in addition to being able to vote or run for office -- they ought to be able to participate in their actions. And I'm not just talking politics here," he said.

"These are people trying to save the lives of Russian citizens. It has nothing to do with promoting democracy or anything like that," Tefft said.